Due to rapid advance of telecommunication technology, cabled network are gradually replaced by wireless network.
When we say WLAN (wireless local area network), an electronic instrument (such as a Personal Computer) can be connected to the WLAN via the Access Point by using a wireless card (generally 802.11g network card) so that the user can browse the web or access the information from the internet. Generally speaking, the WLAN is similar to Ethernet, except that the computer is connected to the WLAN without the cable, but rather by using the wireless network card.
Nowadays, many international airports and international hotels provides the Wireless Access Point services so that the roaming customer can easily connect his notebook computer (or PDA: personal digital assistant) to the Internet for sending e-mails, conducting business communication, browsing the web if the notebook computer is built using WiFi radio technology. In other words, by using the wireless network card access to the Internet is possible via the Access Point.
Note that the wireless network card is generally packed in a shielding device in order to prevent the same from being disrupted by electromagnetic field caused by a nearby electronic instrument. As we all know if somebody uses an electronic instrument (such as hair dryer or mobile phone) nearby while we are watching TV, the latter is susceptible to be disrupted by the electromagnetic field caused by operation of the hair dryer. Under this condition, flickering spots or snowflakes will be formed on the TV screen, thereby blurring the displaying images. Once the operation of the hair dryer is stopped, the images displaying in the TV screen will retrieve their clarity. Electromagnetic interference can therefore degrade and lower the capability of an electronic apparatus.
FIG. 1 shows an exploded view of a conventional shielding device 50 that encloses the wireless network card (not shown) therein and that includes an upper metal plate 12 and a lower metal plate 14. The upper metal plate 12 has a width W1 slightly shorter than the width W2 of the lower metal plate 14. The upper metal plate 12 has two opposite edges and left and right side walls 121, 122 extending downwardly from the opposite edges. Each of the left and right side walls 121, 122 is formed with pluralities of engagement tongues 1211 and engaging holes 1212 that are disposed alternately along the respective edge. The lower metal plate 14 has two opposite edges and left and right side walls 141, 142 extending upwardly from the opposite edges. Each of the left and right side walls 141, 142 is formed with pluralities of engagement tongues 1411 and engaging holes 1412 that are disposed alternately along the respective edge. In order to encloses the wireless network card therebetween, the upper metal plate 12 is press-fitted into the lower metal plate 14 such that after assembly the engagement tongues 1211 of the upper metal plate 12 engage the peripheries defining the engaging holes 1411 in the lower metal plate 14 while the engagement tongues 1412 of the lower metal plate 14 engage the peripheries defining the engaging holes 1411 in the upper metal plate 12 by virtue of slight difference between the widths W1 and W2.
The aforementioned conventional shielding device 50 does provide the wireless network card from being disrupted by the electromagnetic field caused by the nearby electronic instrument. However, disassembling of the same is somewhat difficult due to tight engagement of the tongues 1211, 1412 within the engaging holes 1411, 1211. In case the wireless network card gets out of order and requires repairing, long disassembly time is needed to separate the upper metal plate 12 from the lower metal plate 14.